Patent GB-711943-A (GB)
Title: Frequency control system for electric oscillation generators
IPC: H03J7/22
Filed: 1952-10-28
Abstract: 711,943. Valve generating circuits; adjusting radio apparatus. RADIO CORPORATION OF AMERICA. Oct. 28, 1952 [Nov. 19, 1931] No. 27083/52. Classes 40 (5) and 40 (6). [Also in Group XXXV] In an automatic tuning system for an oscillation generator, the frequency is swept through a wide range until arrested by the response of a frequency discriminator on the desired frequency being attained or passed. The said response also brings into operation a phase discriminator which responds to phase differences between the oscillator output and a reference frequency. Preferably the sweep is reversed in direction and slowed down as the frequency discriminator responds. The system is described in connection with a combined radio transmitter and receiver tunable over a wide range of frequencies, the controlled oscillator being used to derive both the transmitter frequency, and the frequency of the receiving local oscillator. The oscillator output is combined in a series of mixer stages fed by standard reference frequencies, until at the last mixer 51, Fig. 2, it gives an output of 500 kc/s as the swept oscillator frequency passes the desired frequency. Thereupon a resonant circuit 58 is energized and its output is rectified at 59 to provide a position control voltage at the grid of a gas valve 72 and thus to energize an anode relay 73. The opening of contacts 75 operates a motor and clutch mechanism 76 to cause the frequency sweep to be reversed in direction and slowed down. The other contacts 74 of the relay 73 are closed to remove a negative blocking voltage on a grid of a valve 61, which now co-operates with a valve 63 to form a regenerative frequencydivider. The valve 61 is fed by the output of valve 51 at about 500 kc/s, and it output circuit 62, tuned to 50 kc/s, is coupled to the input grid of a frequency-tripler valve 63 which gives a frequency of 150 kc/s in its output circuit 64. This in turn forms a second input to the valve 61 and gives a difference frequency in the circuit 62 of 50 kc/s by the interaction of the 500 kc/s input, and the third harmonic of the 150 kc/s input. The 50 kc/s output is fed to a phasesplitting valve 65, whose output is fed to a phase discriminator comprising four diodes 88 ... 91, to which a 50 kc/s reference frequency of sawtooth form is also fed at A. The DC. output representing the phase error between the two inputs is applied through a cathode follower 67 to a relay valve 98 the anode coil 99 of which controls the tuning motor by contacts 100, 101 so as to centre the tuning of the controlled oscillator on the output characteristic of the phase discriminator. Thereafter, frequency deviation is compensated by a reactance valve associated with the controlled oscillator and having its grid connected to the cathode of the cathode follower 67. In a modified circuit, Fig. 3 (not shown), a frequency discriminator of the Foster-Seeley type is substituted for the resonant circuit 58. The Specification includes a block diagram, Fig. 1b (not shown), of a radio transceiver, in which the frequency of the controlled oscillator is doubled after the subtraction therefrom of 900 kc/s, to provide the transmitter frequency. The local heterodyne oscillation for the receiver is at double the frequency of the controlled oscillator. Another block diagram, Fig. la (not shown), indicates how the various reference oscillations are obtained by frequency dividers and multipliers from a standard oscillator shown as operating at 500 kc/s. The desired frequency is set up on a decade scale, control members being set at positions corresponding respectively to the thousands, hundreds, tens and units of the desired frequency in kc/s. These members select harmonics of the reference frequencies for application to the mixer stages which result in a 500 kc/s output from the final mixer valve 51 when the controlled oscillator is correctly tuned.